I. Field of the Invention
This invention relates generally to pressure transducers. More particularly, this invention relates to a pressure transducer modules which may be connected in-line in a chemically corrosive fluid flow circuit, wherein the pressure sensor used therein is isolated from the fluid flow circuit with a non-contaminating transducer body.
II. Discussion of the Related Art
During the production of semiconductors, the sensitivity to contamination of materials used to produce them is a significant problem faced by semiconductor manufacturers. Various processing systems have been designed to reduce the amount of foreign particles and vapors generated during the processing of these sensitive materials. It is critical that the semiconductor wafers be isolated from damaging particulate and chemicals.
In an attempt to eliminate all sources of damaging contaminants, the equipment used to process the semiconductor wafers has necessarily been designed with this goal in mind. First, the various components of the processing equipment are commonly designed to reduce the amount of particulate generated and to isolate the processing chemicals from contaminating influences. The processing equipment commonly has monitoring and sensing devices connected in a closed loop feedback which are used in monitoring and controlling the equipment. These monitoring and sensing devices must also be designed to eliminate any contamination which might be introduced.
During the processing of semiconductor wafers, highly corrosive hazardous chemicals are commonly used. When these chemicals are used, extremely severe conditions within or near the processing environment may be encountered. Such corrosive atmospheric environments are extremely hard on the monitoring and sensing equipment. Further, the monitoring and sensing equipment may transmit wafer damaging particulate, ions, or vapors as a result of exposure to the corrosive atmospheric environment. Metals, which are conventionally used in such monitoring devices, cannot reliably stand up to the corrosive environment for long periods to time. Hence, the monitoring and sensing devices must incorporate substitute materials.
The highly corrosive environment may be created when hazardous chemicals are delivered to the processing equipment. Liquid transporting systems carry these chemicals from supply tanks through pumping and regulating stations and through the processing equipment itself. The liquid chemical transport systems, which includes pipes, tubing, valves, and fittings and related devices, are frequently made of plastics resistant to the deteriorating effects of the toxic chemicals. Of course, anything mechanical is subject to potential leakage and such leakage can create extremely hazardous conditions both to the processing of semiconductor wafers or other products and also to personnel who may have to tend and maintain the processing equipment. Hence, the chemical transport system must be designed such that leakage is avoided. The monitoring and sensing devices may incorporate sensors which also must be designed to avoid the introduction of particulate, unwanted ions, or vapors into the processing steps.
An in-line mechanical fluid pressure responsive gauge separated from the fluid flow by a protective membrane is known in the art. The gauge is contained within a housing having a cavity filled with a sensor fluid. The cavity is formed adjacent the fluid flow and separated by the protective membrane. The sensor fluid contained within the cavity is typically a silicone oil. A change in pressure within the fluid flow affects the oil pressure within the cavity. The oil pressure is detected by the mechanical pressure responsive gauge.
The fluid within the cavity typically has large thermo-expansions which cause large deflection changes in the protective membrane. The large deflection changes in the protective membrane increases the likelihood that the fluid within the cavity will leak into the fluid flow, contaminating the flow circuit. Also, the accuracy of the pressure gauge is negatively affected by the large thermo- expansions of the sensor fluid. Hence, a need exists for an in-line pressure gauge that does not leak contaminating fluids into the fluid flow circuit. Also, a need exists for a pressure gauge, wherein the accuracy is not affected by thermo- changes within the fluid flow circuit.
Collins et al., in U.S. Pat. No. 5,316,035 (the ""035 patent) describes the use of a capacitance proximity monitoring device in corrosive atmosphere environments. In one embodiment of the ""035 patent, the capacitance proximity device is described as being incorporated into a functional apparatus, such as a valve or coupling for tubing. The capacitance proximity device serves as a functional portion of the apparatus and creates a sensing field within a predetermined area. It is then used to determine the change of electrical characteristics within the predetermined area as various fluids flow past the predetermined area. The current related to the sensing field changes when the liquid target media is present, versus air or gas in the tubing when the liquid target media is absent, thereby producing an indication of the presence or absence of the target media. The complex valving often includes a fluid which may leak into and contaminate the processing fluid flow.
The ""035 patent does not disclose or even consider a device capable of determining various pressures within the chemical transport system of the processing equipment. Monitoring the pressure within the chemical transport system is useful for several reasons. First, a change in pressure within the system may be indicate leakage within the system. Second, the pressure within the transport system is regulated to avoid exceeding predetermined safety limits. Third, the pressure within a fluid flow circuit may be controlled to actuate various processing tools connected to the processing equipment.
Therefore, a need exists for a non-contaminating pressure transducer which may be positioned in-line within a fluid flow circuit carrying corrosive materials, wherein the pressure transducer determines either a gauge pressure or absolute pressure of the fluid flow circuit. A need also exists for a pressure transducer that avoids the introduction of particulate, unwanted ions, or vapors into the flow circuit. The present invention overcomes these and other disadvantages of the related art.
The purpose of the present invention is to provide a pressure transducer module that may be coupled in-line to a flow circuit of corrosive fluid, wherein either the gauge pressure or absolute pressure within the flow circuit may be determined. The pressure transducer module includes a pressure sensor within an non-contaminating body. In the preferred embodiment, the components of the pressure transducer module includes a housing, a cap, an electrical connector, pressure fittings, an isolation membrane, a pressure sensor, electronic circuitry, a spacer ring and a hold down ring.
The cap of the housing is removably attached to the housing by mating threads formed on an internal surface of the cap and on the external surface of the housing. An electrical connector is mounted into the cover, allowing electrical leads within the housing to mate with external conductors when the cover is attached.
The housing has a bore extending therethrough, which forms a passage or conduit through which fluids flow, when the transducer is connected in-line within a fluid flow circuit. Aligned and sealably connected to each open end of the bore are pressure fittings. The pressure fittings are constructed from a chemically inert material and are readily available and known to those skilled in the art. The housing also has a cavity extending from an external surface thereof in communication with the bore. A lip is preferably formed in the housing at the intersection of the cavity and bore. The lip has an inner dimension that is less than the inner dimension of the housing. The isolation membrane, pressure sensor, electronic circuit, spacer ring and hold down ring are all contained within the cavity of the housing.
The isolation membrane is sealed against the lip of the housing within the cavity. In this manner, the cavity of the housing is isolated from the fluid flow. The isolation membrane is preferably constructed of an anti-corrosive, chemically inert material with Polytetrafluoroethylene being preferred. The pressure sensor is bonded, pressed, heat welded or otherwise attached to the isolation membrane. The pressure sensor may be of a capacitance or piezoelectric type. A hybrid or fully integrated electronic circuit disposed in the housing is operatively coupled to the pressure sensor and to the aforementioned connector.
The electronic circuit develops a signal which is a measure of the pressure within the flow circuit from information sensed by the pressure sensor. This electronic circuit may also be used in combination with temperature sensitive components to adjust the pressure measurement based upon temperature changes within the flow circuit. As mentioned, the electronic sensor is coupled by electrical leads to the electrical connector and power may be transmitted to the electronic circuit through the electrical leads mating at the connector with an external power supply. Further, an analog output such as a standard 4-20 milliamps signal proportional to the calculated pressure may be transmitted through additional electrical leads.
The isolation membrane and pressure sensor are contained within the cavity by a combination of the spacer ring and hold down ring. The hold down ring has threading formed on its surface that mates with threading formed on the internal surface of the valve body defining the cavity.
Without limitation, the housing, isolation membrane, spacer ring, and hold down ring are constructed of the same polymer to avoid leakage when the transducer is subject to thermal expansion. In the preferred embodiment tetrafluoroethylene fluorocarbon polymers are used. These polymers reduce the amount of abraded particulate, are chemically inert, and provide a non-contaminating pressure transducer module.
It is accordingly a principal object of the present invention to provide a non-contaminating pressure transducer adapted to be connected in-line in a fluid flow circuit.
Another object of the present invention is to provide a pressure transducer module wherein its pressure sensor component is isolated from the fluid flow circuit by a non-contaminating barrier.
Yet another object of the present invention is to provide a pressure transducer module having an isolation member that is in direct contact with a pressure sensor, the isolation member acting to isolate the sensor and associated electronic circuitry from potentially corrosive processing chemicals and precluding introduction of contaminating substances into the processing fluids being transported.
Still another object of the present invention is to provide a pressure transducer wherein a gauge pressure or absolute pressure of the flow circuit is measured non-intrusively.
These and other objects, as well as these and other features and advantages of the present invention will become readily apparent to those skilled in the art from a review of the following detailed description of the preferred embodiment in conjunction with the accompanying drawings and claims and in which like numerals in the several views refer to corresponding parts.